1. Field of the Invention
The present invention relates to light valve arrays having transversely driven electrooptic gates, and to a method of simultaneously making a plurality of such arrays.
2. Description of the Prior Art
One form of light valve comprises a gate that is electrically addressable for changing the polarization of light passing therethrough, sandwiched between a polarizer and a crossed analyzer. The gate generally comprises a sheet of transparent material exhibiting an electrooptical effect, such as lanthanum doped lead zirconate titanate (PLZT), on which is provided a pair of electrodes for generating an electric field in the material to stimulate the electrooptical effect. In one such light valve array, a sheet of PLZT material has a plurality of coplanar interleaved electrodes formed on one surface of the sheet generally normal to incident plane polarized light, thereby defining a plurality of gates on the sheet. The selective application of electrical voltage signals to adjacent electrodes generates an electrical field in the PLZT material having a component generally perpendicular to the direction of incident light. The plane of polarization of this incident light is at a 45.degree. angle with respect to the perpendicular component of the electrical field. The electric field causes the PLZT material to become birefringent, thereby changing the state of polarization of the incident light. As a result, the transmission of light through the analyzer varies as a function of the strength of the perpendicular component of the electric field in the light valve. For an example of such a light valve array having coplanar electrodes, see commonly assigned U.S. Pat. No. 4,229,095 to Mir. A difficulty with a light valve array having coplanar electrodes is that a signal applied to the coplanar electrodes is inefficient in producing components of the electric fields perpendicular to the incident light, throughout the volume of the light valve gate. Consequently, relatively high voltages are required to operate such light valve arrays. In another approach, U.S. Pat. No. 3,873,187 to Brooks, an array is provided having transversely driven electrooptic gates. Electrodes are provided on opposite parallel surfaces of each gate. The gates are formed by cutting a plurality of parallel grooves in a strip of electrooptical material, and filling the grooves with conductive material, thereby defining a row of gates. Adjacent gates share the electrode between them. Polarized light is incident on a gate surface perpendicular to the plane of the array. Since the electric field produced in the material is uniform throughout the gate volume, the gates can be operated at relatively low voltages. In making such light valves, difficulty is encountered in forming and filling the grooves, especially if the number of gates in the array is large. It is therefore an object of the present invention to provide an improved method of manufacturing light valve arrays having transversely driven electrooptic gates. Another problem with the manufacture of the prior light valve arrays is that of making electrical contact with the electrodes of the array. One known method employs the technique of stringing fine wires through the grooves prior to filling the grooves with conductive material. The wires are bonded to a circuit on which the electrooptic material is mounted. The wire bonding technique, especially for light valve arrays having a large number of gates is time consuming. A further object of the present invention therefore is to provide a light valve array with improved means for making electrical contact with the gate electrodes.
A further problem with the transversely driven light valve array described above, is that each gate electrode is shared by two adjacent gates. As a result, the scheme for addressing the light valve array is complicated. It is therefore a further object of the present invention to provide a transversely driven light valve array having an electrode structure that facilitates simplified addressing.